Process for treating fluid dairy products and product produced thereby



April 9 1957 A. P. STEWART; JR, Erm.. 21,788,283

PROCESS' FR" TRETING `'FLUI DAIRY VPRDUCTS AND PBODQCT FRGDUCED THEREBYFiled Sept. 8.. 1951 2 Sheets-Sheet l HIVIIIHHIII {Illl April 9, 1957 A.P. STEWART, JR., 'ET AL. 2,788,283

PROCESS FOR TREATING FLUID DAIRY PRDUCTS AND PRODUCT PRODUCED THEREBY VEN TORS mi f,

2 Sheets-Sheet :2

MINIMUM SLVE OXYGEN farazbn measured at 25C) 5 l0 l5 Z5 30 35 cfOLVEDOXYGEN (7 SarralorbmeasuREo aT 25C) Filed Sqpt. 8. 1951 www UnitedStates Patent O F PROCESS FOR TREATING FLUID DAIRY PROD- UCTS ANDPRODUCT PRODUCED THEREBY Aubrey P. Stewart, Jr., Berkeley, Donald F.Wilcox,

Gustine, and Robert A. Johnson, San `lose, Calif., assignors, by mesneassignments, to Foremost Dairies, Inc., Oakland, Calif., a corporationrof New York Application September 8, 1951, Serial No. 245,716

5 Claims. (Cl. 99-213) This invention relates to a new and improvedprocess for treating uid milk and cream and the like, according to whicha sterilized nished product is produced which has a concentration ofnonfat constituents which is substantially the same as that of naturalfresh milk or cream, as the case may be, and which possesses a ilavormore closely resembling the flavor of natural milk or cream, and whichat the same time possesses an unusually high resistance to staling.

The term fluid milk products as used hereinafter refers to milk, with orwithout butter fat or other substance also being present and withoutregard to the quantity thereof if present, which has a solids makeup andconcentration substantially the same as that of the nonfat portion ofnatural fresh milk.

An understanding of this invention will be more readily acquired when itis known that for many years attempts have been made `by numerousinvestigators to preserve fluid milk products by methods which willyield products comparable in quality to fresh daily products. Thesemethods have included dehydration, freezing, and sterilizing. In view ofthe fact that the present invention concerns itself with the productionof a sterilized product,

the following discussion will be restricted to prior art practicesinvolving sterilizaton.

In the past, it has been the customary practice to sterilize milk,cream, and evaporated milk in sealed cans. This practice (Condensed Milkand Milk Powder, O. F. Hunziker, 6th edition, 1946, pp. 231 and 232)requires approximately 15 to 20 minutes to raise the temperature of themilk in the can to approximately 240 F.-245 F., thereafter thetemperature is maintained at 240' F.- 245 F. for l5 to 20 minutes andthen the cans are cooled to approximately 70 F. to 80 F. over a periodof approximately 10 to l5 minutes.

This procedure, however, yields products which have so much cookedflavor that their acceptanceby the public, compared with fresh products,is seriously limited. This diilculty arises from the fact thatrelatively high temperatures for long treatment periods are required inorder 2,788,283 Patented Apr. 9, 1957` rfice to cause the heat necessaryfor sterilization to penetrate into the center of the can and therebyreach the entire contents of a can undergoing treatment. Proceduresinvolving the agitation of the can during sterilization treatment havenot permitted the time-temperature ratio to be reduced adequately toavoid a relatively high degree of cooked avor.

It has been recognized for a number of years that cooked flavor may belessened if sterilization were conducted at higher temperatures forshorter periods of time (Condensed Milk and Milk Powder, O. F. Hunziker,6th edition, 1946, p. 254). The practice of this method has not beenwidespread because of diculties hereinafter mentioned, as well as thelack of commercial equipment to aseptically package the sterilizediluid. High-temperature-short-time sterilization is usually conducted bypassing the iiuid through heating equipment designed to quickly raisethe temperature to approximately 285 F. followed by a holding periodsufficient to sterilize the uid. This holding period necessary forsterilization Will vary depending on residence time in passing throughthe sterilizing heater and type of heater, but is usually less than 30seconds. The sterile fluid is then aseptically introduced intopreviously sterilized containers and sealed therein. Apparatus such asthat described in U. S. Patent No. 2,549,216, Apparatus and Method forPreserving Products in Sealed Containers, W. McK. Martin, April 17,1951, may be used.

Notwithstanding the fact that high-temperature-shorttime sterilizationhas been found to reduce the cooked flavor that is developed in theproduct, nevertheless dimculty has been experienced in producing goodquality products by such processes, and as far as is known, thediiliculties so encountered have not been solved except through theprocedures constituting the present invention. The diiliculties referredto are described by B. H. Webb, Food Industries, heat sterilized milkand cream, have a heated (cooked) flavor initially and on storagedevelop a stale ilavor.

Although the cooked flavor of high-temperature-shorttime sterilized milkproducts is considerably less than that of in-the-can sterilizedproducts, it is still objectionable to many consumers. Similarly, thestale ilavor which develops on storage is also objectionable.

A method of processing has now been discovered, according to whichcooked ilavor may be practically eliminated and the development of staleflavor on storage reduced to a point where it is substantiallyundetectable.

This invention proceeds upon the discovery that the substances presentin products of this type which give to the product its cooked avor canbe oxidized, with the result that the objectionable cooked flavor iseliminated,

ilavor substances can be held to a quantity which permits their readyremoval by such oxidation treatment. The

invention is based upon the further discovery that by proper control ofthe oxidizing procedure, according to arcanes Chem., Anal. Ed. 14:641-644 (1942)) may be employed -to measure dissolved oxygenconcentration.

In the following Table I there is shown the correlation betweencooked-avor reducing substances, measured by which the cooked savorsubstances are eliminated, al1 5 the porphyrexide method, and the actualCooked flavor available oxygen present in the product, such as wouldscores measured ofganoiepiicaiiyotherwise substantially react withconstituents of the in Tubi@ H are Shown the amounts of cookediiavofproduct to produce stale avor substances, can be elimreducing substancesProduced by Various high'ieniliel'ninated from the product, with theresult that the finished iufeshori'iinie siefiiiZing conditionsproductis not only free from cooked avor but also is in Tobie iii are shown theamounts of oXYgen re stable with respect to the tendency to develop aStale quired to react with cooked-avor reducing substances 11m/0Lwithout excessive oxygen such as will cause staling.

Accordingly, this invention concerns itself with the in Table IV areshown thcraies ai Which oXYgen controlled and calculated use of oxygento react with reacts With cooked'iievof reducing substancescooked-flavorsubstances produced during sterilization in 15 order to change thesesubstances to substances having a TABLE I is react with the cookedflavor substances, since such excess "educmg Substances as measured bythe pophyrexlde oxygen has been found to result .in 4the development of20 method stale iiavor on storage. Thus, there are two reactionsEvaporated milk, freshly sterilized by conventional ininvolved, asfollows: the-can processing, come-up time l5 minutes to 208 F.,sterilization 245 F. for l2 minutes, cooling 8 minutes yto (A) r 85 F.,was diluted with an equal volume of water.Cooked-Havol--Subs{anCeS-i-Oxygen (reduced f0rm),- 2* The dlilllldeVaPOIated WBS then mlXed II Various non-cooked-ilavor substances(oxidized form) proportions hy Volume With fresh homogenized milk, (B.)HTST pasteurized at 161 F. for 15 seconds, and cooked- Substancesunknown-l-oxygenstale-avor substances iiaVoi' scores assigned asindicated- Reaction A proceeds at a faster rate than does ReactionPorphywxide, B, so that if just suicient oxygen is present in the -milkPercent Percent Reducing to essentially complete Reaction A, thenReaction B will l-feisij -g eglgieass not .take place to any practlcalextent. As a result, 1t is rated Miu: Score mg. Ascorbic possible toproduce heat sterilized mil-k and icream With Acid/Liter practically nocooked liavor and also without the development of a stale flavor. .2 0%.5 In the ,actual lpractice of the invention, analytical tech- 99 10 1j-2l niques are important to determine the amount of oxygen gli g fi- 35required to react with any given amount of cookedgg fl g5 avor reducingsubstances without leaving an excess of B5 3%-1- 48.5 oxygen to producestaling. Accordingly, the porphyrexgg P 5 ide method (A. P. Stewart,Jr., August 1951 issue of 5o 5o sai es Journal of Dairy Science) may beemployed to measure 45 55 Mi' 70'5 cooked-avor reducing substances, andthe polarograph 45 method (G. H. Hartman and O. F. Garrett, Ind. & Eng.

l Porphyrcxide reducing substances includes 10 mg. per liter actualascorbic acid present in pasteurzcd milk.

TABLE II Relationship between hgh-temperature-shot-tme sterilizationconditions and production of cooked flavor reducing substances. Milkdeaerated prior to heating Residence Time (seconds) Residence ReducingTime After Steriliza- Substances In Pre- Between in Dcaera- BetweenOutlet VStcrilizer tion 1 mg,/liter heater Out- Prchentcr tor OutletDeaerator in Sterl- Tempera- Before Cool- Valuc as ascorbic let TemandDeacr- Tcmperaand Sterilizcr turefof lng (sec- Fo acid peratur ator, 190F. ture 17SC F. lizer, 178c F. Stcrilizer, onds) 82 25 29 28 27 270 205. (i 'i4 82 25 29 28 27 280 5 8.9 44 82 25 29 28 27 285 1 10. 2 44 8225 29 28 27 275 23 12. 1 48 82 25 29 28 27 280 11 13. 5 48 82 25 29 2827 285 5 16. 6 48 82 25 29 28 27 290 1 19. 8 48 B2 25 29 28 27 280 2524. 4 52 82 25 29 28 27 285 12 26. 9 52 82 25 29 28 27 290 5 31 52 82 2529 28 27 295 l 34. 5 52 82 25 29 28 27 290 lb 61` 8 58 25 29 28 27 295 874 58 82 25 29 28 27 290 31 104 64 82 25 29 28 27 295 15 111 64lTimc-teniperaturc relationship productive .of sterilization values (Fo)of atleast 5 are considered necessary for sterilization.

TABLE m Relationship between initial cooked-flavor reducing substances,initial dissolved oxygen, final cooked-flavor reducing substances andflavor after storage fluid whole milk Initial Reduc- Dissolved FinalReduc- Calculated Flavor Score 3 ing Substances Oxygen Coning SubstancesFinal 1 Immediately tent Imme- Measured Reducing Test AfterSterilldiately After After Storage Substances Original After 3 monthsNo. zation and Sterilization at 72 F. for (as mg. at 72 F.

Canning (Caland Canning 3 months (as Ascorbic culated as mg, (PercentSatumg. ascorbic Acid per Ascorbic Acid ration at acid per liter) liter)Cooked Stale Cooked Stale per liter) C.)

44 15 24 27 (3+) none.. 1%+ none.

25. 5 19 24 do 1+ v. slight. 43 6. 6 30 28. 5 do..- (2+) none. 45. 5 1129. 5 28. 5 do..- (2+) Do. 45. 5 16. 5 28 27 do.-- 1%-i- D0. 45. 5 25 2524. 5 do 1%+ Do. 45. 5 30. 5 22.5 23 do 1 Do. 45. 5 42 18.5 20 do... 1+(slight). 50 9 29 30. 5 do (2+) none. 50 25 24 26 do... 1%-5- Do. 50 4020 22 do..- 1+ v. slight. 5o 55 15 17.5 do.-- (detente). 53 4 32 33do.-. (2+) none. 53 7 30 32 do (2+) Do. 53 15 29 30 .do (2+) Do. 53 2525 27 do 136+ Do. 53 37. 5 2l 23. 5 do 1+ v. v. slight. 65 5 33. 5 34. 5.do (2+) none. 65 19 32. 5 30. 5 do (2+) D0. 65 31. 5 28 27 ..do 1%+ Do.65 86. 5 26. 5 26 (5+) .do. 11/+ Do. 65 42 22. 5 24 (5+) do 1+ Do.

cent Oz saturation at 25 0.)]

2 Scores in parenthesis indicate flavor regarded to be unsatisfactoryfor good consumer acceptance.

TABLE IV Rate of reaction of cooked-flavor reducing substances withoxygen Cooked- Dissolved Flavor Oxygen, Reducing Test No. Storage Timeat 72 F. Percent Substances,

Saturation mg. /liter as at 25 C. Ascorbic Acid Immediately afterSteril. 42 65 and Canning.

3 days 38. 5

2 Weeks. 27 4weeks.-- 0 22.5 2 months 22. 5 3 months 22. 5 Immediatelyafter Steril. 30. 5 45. 5

and Canning.

3 days 32 7 days.. 9 30 2 weeks- 24 4 Weeks 0 22. 5 2 months.. 22.5 3months 22. 5

Whereas this invention may be practiced according to various proceduralsteps, one satisfactory method which has been found to give good resultswill now be set forth by way of example. This illustrative process maybe better understood by referring lto the accompanying drawings, inWhich-A Figure l is a schematic View in elevation showing apparatusemployed in carrying out the process of this invention.

Figure 2 is a chart on which is shown the minimum, optimum, and maximumamounts of oxygen to be employed in carrying out the present inventionwhen processing Whole milk; and A Figure 3 is a similar chart showingthe minimum, optimum, and maximum amounts of oxygen to be ernployed whenprocessing cream.

Reference to Figures 2 and 3 of the drawing and the line marked Optimumoxygen discloses `that the quantityof free oxygen present in the uid foroperative results may have a value of from substantially `15% saturationto substantially 50% saturation Vat 25 C.

Also referring to Figures 2 and 3, it will be observed that the reducingsubstances or groups are in quantity 5 for operative results of theorder from substantially 25 0 be treated, such as Wholermilk, in tank 1.

mg. to substantially 70 mg. computed as ascorbic acid per liter offluid.

By referring to Figure 1, it will be noted that the invention may bepracticed by placing the 'substance to The milk employed in this examplemay contain 4% butterfat and 8.7% milk solids not fat. The milk is heldin the tank 1 at approximately 40 F. Plfhe tank l is preferablyconnected to a ,three-Way valve 3 which in turn is connected to a Waterline 2 on one side and to a pump 4 on the other side. The discharge ofthe pump 4 leads to a preheater 5, which in this' instance is of thetube and Vshell construction. The discharge of the preheater feeds to adeaerator 6 having a spray nozzle 7 which discharges the liquid into thebody of the deaerator. The top of the deaerator is connected to a vaporlcondenser 8 equipped with a Water spray 9, vacuum pump 16, and a Waterseal line 11. The deaerator discharges at the bottom and is connected toa pump 12 which in turn discharges into a homogenizer 13 which, in thisinstance, is adapted to function at 5000 pounds per square inchpressure.

The discharge of the homogenizer leads to a sterilizing heater 14 whichdischarges into a holding pipe or tube l5. The holding pipe feeds into acooler 16 of the agitated barrel type and thence into a pair of coolers17 and 25, respectively, of the shell and tube type. The line connectingVthe coolers i7 and 2d has a source of air intake connected thereto,which in this instance is represented by the air inlet pipe 22 andowmeter manometer 13 having a fiowmeter orifice 19. ln addition, thereis connected in the line a sterile cotton filter 20 and a. sterileneedle valve 21. The valve 23 is located between the coolers 15 and 17for the purpose of maintaining pressure for sterilizing temperatures.The outlet of the cooler 24 connects directly with the filler head 28 ofan aseptic canning unit, represented generally at 25. At 26 isillustrated the seamer for the aseptic canning unit, and `the positionof the can While being seamed is represented at 27.

The milk stored in tank 1 at approximately 40 F. is

run through the tubular preheater which heats the milk to approximately190 F., immediately following which the milk is sprayed into thedeaerator `6. In this illustration, the vacuum chamber of the deaeratoris maintained at a Vacuum of approximately 161/2 linches of mercury. Thetemperature of the milk is lowered to about 178 F. and becomescompletely deaerated as a result of the above-described treatment. Whenconducted properly, the milk will show 0% oxygen vcontent upon analysis.The deaerated milk is next continuously pumped from the deaerator to thehomogenizer 1.3, where it is homogenized at approximately 5000 pounds ofpressure per square inch. The milk in the homogenizer then continuouslypasses through a steri-lizer heater 14 where the temperature is raisedto approximately 285 F. The milk then passes through a previouslysterilized holding pipe where the milk is maintained at sterilizingtemperature for approximately one second, and from which it passes intoa'previously sterilized cooler. In this instance, the cooler isrepresented by the barrel `cooling device 16 and the tube and shellcooler 17.

Under the conditions above set forth for sterilization and taking intoaccount the come-up time and type of heater employed, the sterilizationvalue produced was Fo=10.2. This sterilization value is safely abovethat which is necessary to insure complete sterilization of the milk,

According to the teachings of this invention, based on priorexperimental and test work, it is now known that under such conditionsthe amount of cooked ilavor reducing substances present would beapproximately 44 mg. per liter (see chart in Figure 2). Accordingly,sterile air is injected into the milk at the inlet to cooler 24, withthe rate of air addition being controlled by needle valve 21 andmeasured by Hou/meter 18 in such manner as to cause the milk to becomebetween 25% and 35% saturated with oxygen, when measured at 25 C. The25% to 35% saturation value is determined by the showing of the chart inFigure 2 and represents the amount of oxygen discovered to be sutiicientto react with 44 mg. per liter cooked flavor reducing substances to theextent that the cooked flavor will be lowered to the point where it isnot objectionable to the consumer, yet at the same time thc amount ofoxygen so selected is not excessive such as would cause the developmentof stale avors upon storage for several months, After the addition ofair in the desired quantity, the milk is further cooled to approximately60 F. in the previously sterilized tubular cooler 24, and is then cannedaseptically in a suitable aseptic canning machine. the machine describedand claimed in United States Letters Patent No. 2,549,216, issued April17, 1951, to William Martin has been employed with success.

Milk processed as above described, when analyzed, showed a finishedcanned product 26% saturated with oxygen when measured at 25 C., andcontained 44 mg. of reducing substances per liter. On storage at 72 F.,the amount of reducing substances remaining after re` action with theoxygen present was 23 mg. per liter, which reaction was essentiallycomplete in three weeks. The cooked avor after three weeks storage andthereafter for storage periods up to six months (which was the extent ofthe test) at 72 F. was judged to be 1+, or so slight as to be consideredacceptable to most consumers for beverage purposes. Furthermore, nostaling could be detected from samples stored for four months at 72 F.and only very slight staling could be noticed after 6 months of storageat 72 F. The very slight staling present after six months of storage wasjudged to be unobjectionable and undetectable by the average consumer.

Sterilization conditions can be altered if desired to give initialreducing substance values of from 42 mg. to 70 mg. per liter andthereafter air added as desired within the limits illustrated in thecharts of 'Figures 2 and 3. In such case, the milk preferably would bede- In this particular instance, f

it is to be understood tha-t pure oxygen may be used instead of air,provided it is employed in ,equivalent amounts.

it not necessary to completely deaerate the milk prior to sterilization.When this is not done, the amount of reducing substances in the milkleaving the sterilizer Vis lower than when the milk is first completelydcaerated. Iltis is because the reaction of reducing substances withoxygen occurs simultaneously with the production of such substancesduring sterilization. When milk is sterilized without first completelydeaerating it, the amount of air or oxygen needed to be injected issomewhat less for le reason that the reducing substances present areless. then necessary to determine the reducing substances present aftersterilization and make certain that the proper amount and only theproper amount of oxygen is present to react with these reducingsubstances.

Thus it is a possibility to partially deaerate, or to deaerate andinject air, prior to sterilization so that the amount of air reactingduring sterilization plus that reacting after sterilization is sufcientto reduce cooked flavor but not in excess to cause staling. The properamount of oxygen can always be calculated by means of the data set forthin this disclosure.

Deaeration before sterilization and injection of air or oxygen aftersterilization provide the following benents- (a) Sterilization in thepresence of air or oxygen is more destructive of vitamin C (ascorbicacid) as compared with 72 F. storage in the presence of air or oxygen;and

(b) Deaeration after sterilization avoids the use of sterile deaerationequipment, which is more ditlicult to manage.

Also, it is preferred to use sterilization conditions which produce lessamounts of reducing substances than to use excessively high temperaturesand longer holding times, or either thereof, which produce largeramounts of reducing substances. In other words, it is better to usesterilizing conditions which are not excessively greater than thoserequired to sterilize the product. The reasons for this preferentialtreatment are- (a) Excessive heat is likely to give a brown color to themilk; and (b) there is some indication that when initial reducingsubstances are high and necessitate high additions of air or oxygen toproduce the oxidized or non-cooked haver form, the relatively largeamounts of this oxidized form can in turn react with substances in milkto give stale avor. At least it has been noticed that when initialreducing substances are high, for example, above 60 mg. per liter, it ismore diicult to achieve a satisfactory low cooked flavor without stalingoccuring in storage. This latter ditiiculty is quite noticeable at mg.per liter.

In the practice of this invention, the following formula can be used incalculating the reaction of milk:

[Final R. S.] [Original R. S.] X [l: (.0068 X Original R. 8.] [.28(percent O2 saturation at 25 C.)]

This invention, however, may be applied to various types of product,such as milk and cream or similar dairy products. Inasmuch as somevariation in the process is indicated as applied to cream, some commentson this subject will now be made.

essere The same basic factors established for' whole' have been found toapply to the processing of cream,A with the following alteration: Creamas here used means a product containing approximately 18% butterfat.

Oxygen is more efficient in reacting with reducing substances in cream,and therefore less oxygen is required when processing cream than whenprocessing milk. The chart of Figure 3 gives the amount of oxygenrequired for the best results when processing cream. For cream havingless than 18% butterfat, say, for instance, 11.7% fat as in the productcommonly termed half-and-half, the amount of oxygen to be employed wouldreside midway between the quantities illustrated in the charts ofFigures 2 and 3, respectively, for any particular initial reducingsubstance level.

The following formula can be used in calculating the relationshipbetween original reducing -substances and the amount which will reactwith oxygen:

[Final R. S.] [Original R. S.l i l (.0068 X Original R. S.)] [.6(percent Oz saturation at 25 0.)]

In addition to the foregoing, it should be known that hydrogen peroxideinjections in the milk have been found to function in a manner similarto air tor oxygen, insofar as lowering the cooked flavor without stalingis concerned. However, the use of hydrogen peroxide is not assatisfactory since there is a tendency for the H2O2 to cause the milk tohave a brownish-pink colorand to give to the milk a foreign tastesimulating sunlight flavor. The creation of sunlight flavor isparticularly noticeable at high levels of addition. One advantage,however, resulting from the use of H2O2 is that the reaction of thereducing substances is more rapid than is the reaction produced byoxygen.

Applicants are aware of the fact that copper sulfate, as has beenreported in the literature, is a substance capable of reacting withcooked flavor reducing substances. However, the use of copper sulfate isnot satisfactory for carrying out this invention, particularly at levelsof high addition (2 p. p. m.), since it gives a foreign taste simulatinga sour taste. However, Cu++ may be used in small amounts to catalyze thereaction of reducing substances with oxygen.

It may be theoretically possible in some instances, where the practiceis to deaerate and can air-free liquid, that air be introduced into theaseptic canning equip ment and become part of the headspace. This aircould possibly be in correct amounts to react with the reducingsubstances on storage in a similar manner to when the air is injectedinto the milk prior to canning. However, this would be more difficult toachieve since exact control of the proper ratio between air in theheadspace and liquid volume is difficult.

It should be stated that even in the absence of air or oxygen there issubstantial loss in cooked flavor during storage which can also bedetermined by porphyrexide reducing substance analysis. However, thisdecrease in cooked flavor must be supplemented by reaction with oxygento achieve sullciently low cooked flavor in most instances. The formulasgiven on pages 17 and 18 and the charts of Figures 2 and 3 take intoaccount both the decrease in reducing substances (cooked flavor)occurring from reaction with oxygen and from other reactions notrequiring the presence of free dissolved oxygen.

In all cases where reference is made to porphyrexide reducingsubstances, the natural ascorbic acid in the milk is included in thevalues. ln the cases of whole milk and cream on which our data weredeveloped, the natural reduced ascorbic acid content was 12.5 to 16 mg.per liter, lluid skim milk basis, or, in other words, 12.5 to 16 mg. per90 grams milk solids not fat, in the freshly prepared sample beforestorage. The average was 14 mg. The rest of the reducing substances (thetotal minus reduced ascorbic acid)"co`nstitntes true' cooked llavorreducingl substances.

4It was believed best to include reduced ascorbic acid in theporphyrexide reducing substance values, however, since it was found thatthe reduced ascorbic acid in milk influences the amount of oxygenrequired to reduce cooked flavor. This is in spite of the fact that each10% of dissolved oxygen in milk will oxidize only about 0.5 mg. reducedascorbic acid per liter at 72 F. storage and thus, by our preferredprocedure the reduced ascorbic acid retention is considered excellent.

If anyone should use milk with higher or lower natural ascorbic acidcontent, the calculations for amount of oxygen required, based on totalreducing substances, should still be valid.

It is the usual practice to withdraw the air in the head space of thecan when the finished product is canned. lnthis way, no oxygen or air isleftrin contact with the product over and above'that which has beenintroduced by the procedure constituting this' invention. vlt is to beunderstood, however, that instead of following the usual practice ofremoving the air in the head space, predetermined amounts of air can beleft in the head space provided that allowance is made therefor duringthe practice of the invention. It is found that when air is left in thehead space of the cans it ultimately reacts with the reducing substanceson storage in a manner similar to that which occurswhen the air isinjected into the milk prior to canning.

In the following claims, vreference is made to reducing substancesproduced in the product as a result of the sterilization treatment, andit is the reducing substances so produced which are responsible for thecooked flavor and which are to be eliminated by the oxidizing processcharacteristic of this invention. Accordingly, reference in the claimsto reducing substances produced as a result of the sterilizationtreatment is not to be construed as including naturally present ascorbicacid, and therefore the claims are to be read on a basis excluding fromthe quantities of reducing substances referred to, the quantities ofnatural ascorbic acid present.

In the following claims reference is made to free oxy gen and it is tobe understood that this term includes all forms and sources of freeoxygen including molecular oxygen as well as air and otheroxygen-bearing gases.

What is claimed is:

1. The process of rendering fluid milk products sterile and at the sametime relatively free from cooked. avor and the tendency to ydevelop astale ilavor which comprises deaerating the lluid to substantially freeit from oxygen, homogenizing the deaerated fluid, sterilizing the fluidby raising the temperature to above 265 F., holding it at suchtemperature for a period of time, less than two minutes, such as issufficient to produce an F. value above 5, cooling the fluid and addingoxygen thereto substantially equivalent to the predetermined cookedflavor producing reducing substances present which are created by thesterilization and sealing the treated uid in sterile containers underaseptic conditions.

2. The process of rendering fluid milk products sterile and at the sametime relatively free from cooked flavor and the tendency to develop astale flavor which comprises preheating the fluid product to atemperature of approximately F., deaerating the fluid to substantiallyfree it of oxygen, homogenizing the deaerated fluid, sterilizing thefluid by raising the temperature thereof to approximately 285 F. for aperiod of the order of eight seconds, cooling the fluid and addingoxygen thereto substantially equivalent to the predetermined cookedflavor producing reducing substances present which are created by thesterilization and sealing the treated fluid in a sterile container underaseptic conditions.

3. The process of rendering uid milk sterile and at the same timerelatively free from cooked avor and the tendency to develop a staleavor, which comprises preheating lthe Huid milk to a temperature .ofapproximately 190 F., deaerating the fluid to substantially free it fromoxygen, homogenizing the vdeaerated fluid, sterilizing the uid byraising the :temperature thereof to about 285 F. and for a time suchthat sterilizing .conditions are productive of an Fo of about 10.,adjusting the rel1ationship between the quantity of reducing substancespresent which are created by .said sterilization treatment and theyquantityot free oxygen so .tnat they are .substantially equivalent, 18%to 30% saturation with oxygen being optimum, and sealing the treatedliuidrnilk in sterile container with said free oxygen to rcombine withthe reducing substances to diminish the free .oxygen vto a quantityinsuci-ent to oxidize substances productive, when oxidized, of staleilavor in such .quantity :as will rcsult in the development of a staleflavor in said product.

4. The process of rendering uid milk products sterile and at the sametime ,relatively free from cooked tavor and the tendency to develop astale avor which comprises partially deaerating the uid to reduce thecontent of free oxygen to an amount less than sutlcient to oxidize thereducing substances created by the subsequent sterilization step,sterilizing the fluid by high temperature short time sterilization to anFo of at least 5, cooling the fluid and adding oxygen thereto to thatpresent in the Huid so that the total oxygen present is substantiallythat required to oxidize the predetermined cooked lavor producingreducing substances present created by theA sterilization and sealingthe treated fluid in sterile containers under aseptic conditions.

5. The process of rendering fluid milk products sterile.

and at the same time relatively free from cooked flavor andthe tendencyto develop a stale flavor, which comprises `the steps of adjusting thequantity of free oxygen presen-t in said uid'to a value of fromsubstantially 15% saturation to substantially saturation, andsterilizing the milk product, prior to canning, by heating the same to atemperature not lower than 265 F. for a period of time productive of anFo value of at least substantially 5, 'and producing as a result of suchsterilization, reducing groups in quantity in the order of fromsubstantially 25 mg. to substantially 70 mg., computed as ascorbic acidper liter of vfluid, with the result that the free oxygen present issuiicient to oxidize said reducing groups to an extent materially toreduce the cooked avor produced by said sterilization treatment and yet,upon substantial completion of said oxidation, any free oxygenremaining, is insuicient in quantity to oxidize substances productive,when oxidized, of stale flavor in such quantity as will result in thedevelopment of a stale avor in said product, and finally sealing thetreated uid in sterile containers under aseptic conditions.

References Cited in the le of this patent UNITED STATES PATENTS BakerSept. 20, 1949

1. THE PROCESS OF RENDERING FLUID MILK PRODUCTS STERILE AND AT THE SAMETIME RELATIVELY FREE FROM COOKED FLAVOR AND THE TENDENCY TO DEVELOP ASTALE FLAVOR WHICH COMPRISES DEAERATING THE FLUID TO SUBSTANTIALLY FREEIT FROM OXYGEN, HOMOGENIZING THE DEAERATED FLUID, STERILIZING THE FLUIDBY RAISING THE TEMPERATURE TO ABOVE 265*F., HOLDING IT AT SUCHTEMPERATURE FOR A PERIOD OF TIME, LESS THAN TWO MINUTES, SUCH AS ISSUFFICIENT TO PRODUCE AN F, VALUE ABOVE 5, COOLING THE FLUID AND ADDINGOXYGEN THERETO